Francesco D’Aiuto: ‘People should not underestimate what the body senses when the mouth is neglected.’
Photograph: Mladen Mitrinovi/Getty Images

As daily rituals go, it’s up there with getting dressed. Whether you brush your teeth to avoid cavities or bad breath, a clean, bright smile is a social necessity. Yet, a quarter of British adults don’t brush the recommended two times a day, and one in 10 regularly forget to brush altogether. Painful trips to the dentist and missing teeth are the obvious consequences. But what about heart disease, diabetes or cancer?

The idea that bacteria or inflammatory chemicals released by immune cells in the gums can enter the bloodstream and influence the behaviour of other tissues or organs is known as the mouth-body connection. “The mouth is not disconnected from the rest of the body,” says Francesco D’Aiuto, senior lecturer at the Eastman Dental Institute in London. Although it’s too early to say for sure that gum disease directly causes other more serious illnesses, “people should not underestimate what the body senses when the mouth is neglected”.

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The mouth-body connection is not a new idea. Indeed, Hippocrates attributed a case of arthritis being cured to the pulling of a tooth. In 1900, a British doctor called William Hunter proposed that so-called “focal infections” in the teeth and gums were a cause of disease elsewhere in the body; Hunter’s theory was a key reason why so many people used to have their teeth extracted deliberately. As recently as 1968, when the UK’s first adult dental health survey was carried out, nearly three-quarters of adults over 55 had none of their own teeth.

In the past decade, there has been an explosion of new research linking oral health to illnesses such as Type 2 diabetes, cancer and heart disease. The most likely explanation is inflammation; the same heat, swelling and discomfort you experience when you stub your toe or get an infected splinter, only in this case it isn’t switched off. Such chronic inflammation can be damaging to cells and the DNA they contain. “Inflammation seems to be associated with far more diseases than we’ve traditionally thought,” says Francis Hughes, professor of periodontology at King’s College London.

So, where does this inflammation come from? One of the main reasons we brush is to remove plaque, a sticky matrix of bacteria and the waste materials they secrete. Plaque is bad news for several reasons: some of the bacteria living in it produce acid that erodes tooth enamel and causes cavities. But other types of bacteria also flourish within plaque, and they can trigger inflammation in the tissues surrounding the teeth. “The bacteria that cause gum disease like to be buried deep down in areas where there isn’t any oxygen, so if you have thick bacterial plaques, they like that,” says Hughes.

In its early stages, gum disease manifests itself as gingivitis, or bleeding when you brush your teeth. Left untreated, this can develop into periodontitis, where the gum begins to pull away from the tooth, allowing bacteria to grow in this newly-formed pocket. “When you have gum disease, the gums are effectively ulcerated inside, so they’re not forming a tight seal. Every time you eat or brush your teeth, it pushes bacteria into the body and triggers inflammation,” Hughes explains.

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Perhaps the strongest mouth-body association found so far is between gum health and cardiovascular disease. In 2007, D’Aiuto published a paper in the New England Journal of Medicine suggesting that deep-cleaning teeth and gums under local anaesthetic resulted in healthier, more elastic arteries six months later. Then, in 2012, the American Heart Association published a statement confirming that periodontal disease is associated with atherosclerosis – a condition whereby arteries become clogged up by fatty substances – even after common causes such as socio-economic factors and smoking are taken into account.

Despite such evidence, it’s still possible that gum disease doesn’t directly cause heart disease. Another possibility is nutrition, suggests Richard Watt, chair of dental public health at University College London: “If you’ve got pain and inflammation, you can’t chew as well, so this may limit your consumption of fruit, vegetables and cereals.”

There is also emerging evidence of a direct link to diabetes. In May, D’Aiuto published a study in PLoS One assessing the impact of treating gum disease in people with Type 2 diabetes. It concluded that gum treatment reduced general levels of inflammation, which could have implications for patients’ ability to control blood glucose. Other small studies have hinted that periodontal therapy may actually lower blood-sugar levels in people with Type 2 diabetes.

The links between gum disease and cancer are more circumspect. “It’s plausible, but it’s not at all clear what the precise mechanism might be,” says Hughes. Chronic inflammation is one possibility; it makes cancer-causing mutations more likely to occur, and it may also fuel cell-division. But a study published in Immunity earlier this year also hinted that a bacterium implicated in gum disease, Fusobacterium nucleatum, can reduce the ability of the immune system to recognise and destroy cancer cells.

So, what message should we take from these studies? Most experts agree that twice-daily brushing with a fluoride toothpaste is the best route to healthy teeth and gums, combined with regular trips to the dentist. But which dental health products should you spend your money on? According to the Cochrane Oral Health Group, an international network that reviews the evidence for dental treatments, electric toothbrushes are more effective than hand-brushing, while the evidence for flossing or interdental bushes is pretty weak.

“If you were to choose a toothbrush it would be a power toothbrush, ideally with a rotating oscillating action, and if you were to choose a toothpaste it would be one containing 1,500ppm fluoride and an antibacterial agent called triclosan,” says Helen Worthington, director of evidence for practice at the group. Her advice is worth heeding. While most of us simply want clean, bright, healthy teeth because they look nice, the adage that, if you look after your teeth, they will look after you, has never seemed truer.